This proposal requests continued support for a program of empirical and theoretical research on speech perception and spoken word recognition. The major goal of this project is to seek a better understanding of the earliest stages of speech processing. We are interested in how the initial acoustic-phonetic information in the speech waveform interacts with other sources of knowledge to support spoken language understanding. The proposed research will involve behavioral studies, computational analyses using large computerized databases and modeling techniques to gain new knowledge about the perceptual and cognitive processes that human listeners use in perceiving words, sentences and passages of connected fluent speech. The proposed studies are divided into four major projects: (l) spoken word recognition and the mental lexicon; (2) contextual variability in speech perception and spoken word recognition; (3) perceptual learning and adaptation, and (4) real-time comprehension. From these projects, we hope to learn more about how speech signals are encoded and processed by the nervous system and how the earliest stages of speech perception are interfaced to the more abstract linguistic and cognitive processes used in spoken language understanding. The findings from this research project have implications for normal language functioning as well as for the diagnosis and treatment of communicative disorders in adults and children.